Recently, information society has been rapidly developed, and home networking has been rapidly popularized. Under such a situation, a plurality of apparatuses connected to a home network cooperate with each other, and operate while communicating with each other, whereby convenience of services provided by the apparatuses is expected to be improved.
Further, since the apparatuses connected to the home network are used by a home user, work of connecting the apparatuses need to be as simple as possible.
However, the home user does not have enough knowledge about network. Thus, the home user may not tell the difference between a router and a hub, and may connect a router instead of a hub, or connect a wireless router instead of a wireless access point. Further, the home network often includes a plurality of routers, and a failure that communication between the apparatuses is disenabled to be performed may occur due to this network configuration. In order to prevent this, the user needs to understand the configuration of the home network, and needs to connect an apparatus for performing communication at a position in a network at which communication is possible. However, this is not realistic. It is noted that although a home network is described as an example of a local network here, there are a small number of people having special knowledge even in a company, and much the same is true on an intranet.
Impossibility of communication between apparatuses in the case where a home network includes a plurality of routers will be described in detail using a drawing. FIG. 31 shows an example of a configuration of a home network 52 including a plurality of conventional routers. As shown in FIG. 31, a router 53b and a router 53c are connected under a router 53a having a built-in modem. A router for home use has a NAT function and a firewall function. Thus, in the case where the home network 52 includes the plurality of routers, an address translation (NAPT) function and a firewall function are activated in the home network 52. Generally, with a home router, because of a NAPT function and a firewall function, communication cannot be started from an apparatus located on a WAN side to perform communication with an apparatus located on a LAN side. Thus, in the example of FIG. 31, communication cannot be started from a communication apparatus to a communication apparatus 55b. 
It is noted that since communication from the communication apparatus 55b to the communication apparatus 55a is communication from a LAN side to a WAN side for the router 53b, address translation (NAPT) setting is automatically performed with respect to the router 53b. Thus, it is possible to perform communication from the communication apparatus 55b to the communication apparatus 55a. 
For such a problem that communication is disturbed by the home router, there is known a method in which a connection assistance server is provided outside the home network (e.g. on the Internet), and a communication apparatus on a WAN side of a router connects to the home network to a communication apparatus on a LAN side thereof via the connection assistance server (e.g. the Patent Document 1). In this method, a communication apparatus in the home network establishes a communication path to the connection assistance server. Then, a communication apparatus outside the home network connects to the communication apparatus in the home network via the connection assistance server.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2003-169075
However, the method using the conventional connection assistance server assumes that the connection assistance server is provided outside the home network, and there is a problem that the method cannot be used unless the home network is connected to an external network (e.g. the Internet).
Here, a case where the conventional connection assistance server is provided in the home network is considered. In such a case, it is assumed that the connection assistance server is installed by a user who does not understand the network. Thus, a desired function needs to be achieved even when the connection assistance server is connected to any position in the home network.
In other words, the method using the conventional connection assistance server is usable for the communication apparatus in the home network only when the connection assistance server is always located in a position on the Internet side (the WAN side). Thus, there is a problem that the conventional method cannot be used in a home network including one or more routers connected in series.
For example, in the case where the connection assistance server is connected to the home network including one or more routers connected in series as shown in FIG. 31, since it is not taken into consideration that the connection assistance server is connected to a network (a multi-segment network) including a plurality of routers for the conventional method, when the connection assistance server is connected to the router 53b and the router 53c, the communication apparatus 55a cannot connect to the connection assistance server. In other words, there is a problem that a communication path between the communication apparatus 55a and the connection assistance server cannot be established depending on a position where the connection assistance server is installed.